I. V. Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials (Kola Science Center RAS), Apatity, Russia:
P. B. Gromov, Deputy Director for Science, e-mail: gromov@chemy.kolasc.net.ru
M. A. Muzhdabaeva, Researcher
E. K. Kopkova, Senior Researcher
N. V. Serba, Leading Technologist

Our paper shows the possibility of rare metals extraction during low-temperature decomposition of bismutotantalite concentrate (t_start = 20 ^oC) by the solutions HF and HF + H₂SO₄. Concentration of fluorohydric and sulfuric acids and volume of acid reagent are the main technological parameters, defining the completeness of tantalum and niobium extraction from bismutotantalite concentrate. The process time makes a lesser influence on the process itself. A different solubility of formed fluoride compounds allows the separation of fluorcomplex compounds of tantalum and niobium from non-soluble fluoride compounds of bismuth on decomposition stage. We defined the conditions of efficient decomposition of bismutotantalite concentrate, providing 97–99% of niobium and tantalum extraction in solution and 160–190 g/l of their concentration in solution. Having an interaction of bismutotantalite concentrate, both with fluorohydric acid and with mixed acid reagent, bismuth and natural radionuclides U (IV) and ThO₂ (>98%) are released as low-soluble fluoric compounds and are concentrated in insoluble bismuthbearing fluoride cake. We found the conditions, where a high total content of niobium and tantalum is reached in industrial solutions (≤190 g/l), which enables the considerable decrease of concentration of fluorohydric acid (≤173 g/l) for further efficient extraction processing of solutions. After correction, the prepared solution may be sent to decomposition of niobium and tantalum according to the flowsheet of bulk extraction of niobium (V) and tantalum (V) by n-oktanol with their decomposition on re-extraction stage. In total, low-temperature decomposition of bismutotantalite concentrate allows the decrease of the process's energy intensity at high indicators of tantalum and niobium extraction in liquid phase, and decrease the losses of volatile components (HF, SiF₄), which significantly improves the ecological characteristics of this technology.

1. Krenev V. A., Drobot N. F., Fomichev S. V. Processes of bismuth extraction from ores and concentrates. Khimicheskaya tekhnologiya. 2014. No. 5. pp. 304–308.
2. Krenev V. A., Drobot N. F., Fomichev S. V. Bismuth: areas of use and global market. Khimicheskaya tekhnologiya. 2014. No. 1. pp. 42–46.
3. Lebedev V. N., Masloboeva S. M., Voloshin A. V., Kalinnikov V. T., Masloboev V. A., Melnik N. A. Decomposition of plumbomicrolite concentrate by mixture of fluorohydric acid, sulfuric or hydrochloric acid. Khimicheskaya tekhnologiya. 2006. No. 11. pp. 32–35.
4. Masloboeva S. M., Lebedev V. N., Melnik N. A., Arutyunyan L. G., Kalinnikov V. T. Investigation of conditions of plumbomicrolite concentrate decomposition by mixture of fluorohydric and nitric acids. Tsvetnye Metally. 2007. No. 8. pp. 78–81.
5. Zelikman A. N., Korshunov B. G. Metallurgy of rare metals. Moscow : Metallurgiya, 1991. 431 p.
6. Maslov A. A., Ostvald R. V., Shagalov V. V., Maslova E. S., Gorenyuk Yu. S. Chemical technology of niobium and tantalum. Tomsk : Izdatelstvo Tomskogo politekhnicheskogo universiteta, 2010. 97 p.
7. Ayanda O. S., Adekola F. A. A review of niobium-tantalum separation in hydrometallurgy. Journal of Minerals and Materials Characterization and Engineering. 2011. Vol. 10, No. 3. pp. 245–256.
8. Eckert J. Hydrometallurgical processing of tantalum and niobium compounds. Proceedings of International Symposium on Tantalum and Niobium (Goslar, 18–20 August 1995). Goslar, 1995. pp. 51–64.
9. Mayorov V. G., Kopkov V. K., Baklanova I. V., Baltsat V. I., Mimonov A. V., Nikolaev A. I. Technology of processing of columbite concentrate of Malishevskoe mine group. Khimicheskaya tekhnologiya. 2000. No. 7. pp. 23–27.
10. Mayorov V. G., Nikolaev A. I., Kopkov V. K., Elizarova I. R. Processing technology for tantalite (Kongo deposit) and columbite (Zashikhinskoe deposit). Khimicheskaya tekhnologiya. 2015. Vol. 16, No. 1. pp. 23–27.
11. Nikolaev A. I., Mayorov V. G., Kirichenko N. V. New in extraction technology of separation of niobium and tantalum. International symposium on sorption and extraction, 29.09–4.10, 2008. Vladivostok. pp. 22–26.
12. Koznov A. V., Kozyrev A. B., Nechaev A. V., Seleznev A. O., Sibilev A. S., Smirnov A. V., Sokolov V. D. Method for columbite concentrate processing. Patent RF, No. 2576562. Applied: 25.11.2014. Published: 10.03.2016.
13. Lidin R. A., Molochko V. A., Andreeva L. L. Chemical properties of inorganic substances. Moscow : Khimiya, 1996. 480 p.
14. Ripan R., Chetyanu I. Inorganic chemistry. Vol. 1. Moscow : Mir, 1971. 560 p.